Technologies for viscosity reduction of heavy crude oils and resids are of importance to the upstream and downstream petroleum businesses respectively. In downstream refining operations, visbreaking and hydro-visbreaking (visbreaking with hydrogen addition) of resids are known in the art and practiced commercially. In the upstream production operations, crude oil dilution with gas condensate and emulsification technologies using caustic and water are some of the commonly practiced art in pipeline transportation of heavy oils e.g., bitumen. Moreover, viscosity reduction of heavy crude oils can play a role in new upstream technology related to recovering hydrocarbons from subterranean formations using enhanced oil recovery methods. There is a continuing need in the oil industry for technologies and technology improvements relating to viscosity reduction of crude oils and resids.
The depletion of reserves containing high quality crude oil, and the accompanying rise in costs of high quality crude oil has producers and refiners of petroleum looking to heavy crude oil reserves as a source for petroleum. There are many untapped heavy crude oil reserves in a number of countries including Venezuela, Chad, Russia, the United States and elsewhere. However, these heavy crude oils, because of their high viscosity and poor flow properties, pose significant challenges to producers, transporters and refiners of oil. Heavy crude oils are often difficult if not impossible to extract from subterranean formations in an efficient and cost-effective manner. Further, even when the heavy crude is extracted, the poor flow characteristics of the crude oil present additional complications in pumping, transporting and refining the crude oil.
Processes have been developed to aid in extracting the heavy crude from underground reservoirs. For instance, a new process has recently been developed which aids in extracting heavy crude oil from a subterranean formation, which uses solids-stabilized emulsions as a driver fluid or as a barrier fluid to help recover hydrocarbons from the subterranean formation. These methods are generally discussed in U.S. Pat. Nos. 5,927,404, 5,910,467, 5,855,243, and 6,068,054. U.S. Pat. No. 5,927,404 describes a method for using the novel solids-stabilized emulsion as a drive fluid to displace hydrocarbons for enhanced oil recovery. U.S. Pat. No. 5,855,243 claims a similar method for using a solids-stabilized emulsion, whose viscosity is reduced by the addition of a gas, as a drive fluid. U.S. Pat. No. 5,910,467 claims the novel solids-stabilized emulsion described in U.S. Pat. No. 5,855,243. U.S. Pat. No. 6,068,054 describes a method for using the novel solids-stabilized emulsion as a barrier for diverting the flow of fluids in the formation. In a solids-stabilized emulsion, the solid particles interact with the surface-active components in the water and crude oil to enhance the stability of the emulsion. The process is simple in that the emulsion is made by simply mixing oil, typically crude oil from the reservoir itself, with micron or sub-micron sized solid particles and mixing with water or brine until the emulsion is formed. The process is also cheap in that all of these materials should be readily available at the reservoir site.
Solids-stabilized water-in-oil emulsions have a viscosity that is greater than that of the crude oil to be recovered, and as such, can serve as an effective drive fluid to displace the crude oil to be recovered, such as described in U.S. Pat. Nos. 5,927,404, and 5,855,243.
The solids-stabilized water-in-oil emulsions can also be used as a barrier fluid, to fill in subterranean zones of high rock permeability, or “thief zones.” When drive fluid is injected into a reservoir, the injected drive fluid may channel through these zones to producing wells, leaving oil in other zones relatively unrecovered. A high viscosity barrier fluid, such as the solids-stabilized water-in-oil emulsion, can be used to fill these “thief zones” to divert pressure energy into displacing oil from adjacent lower-permeability zones.
However, sometimes the solids-stabilized water-in-oil emulsion is too viscous to be injected or is too viscous to otherwise be efficiently used as a drive or barrier fluid. Therefore, there is a need to be able to reduce the viscosity of the emulsion to obtain the optimum rheological properties for the type of enhanced oil recovery method used and for the particular type and viscosity of crude oil to be recovered
Viscosity reduction of heavy oils is also important for downstream operations. Transporters and refiners of heavy crude oil have developed different techniques to reduce the viscosity of heavy crude oils to improve its pumpability. Commonly practiced methods include diluting the crude oil with gas condensate and emulsification with caustic and water. Thermally treating crude oil to reduce its viscosity is also well known in the art. Thermal techniques for visbreaking and hydro-visbreaking are practiced commercially. The prior art in the area of thermal treatment or additive enhanced visbreaking of hydrocarbons teach methods for improving the quality, or reducing the viscosity, of crude oils, crude oil distillates or residuum by several different methods. For example, several references teach the use of additives such as the use of free radical initiators (U.S. Pat. No. 4,298,455), thiol compounds and aromatic hydrogen donors (EP 175511), free radical acceptors (U.S. Pat. No. 3,707,459), and hydrogen donor solvent (U.S. Pat. No. 4,592,830). Other art teaches the use of specific catalysts such as low acidity zeolite catalysts (U.S. Pat. No. 4,411,770) and molybdenum catalysts, ammonium sulfide and water (U.S. Pat. No. 4,659,453). Other references teach upgrading of petroleum resids and heavy oils (Murray R. Gray, Marcel Dekker, 1994, pp.239-243) and thermal decomposition of naphthenic acids (U.S. Pat. No. 5,820,750).
A common thread that knits the various methods previously described is a need to obtain optimum viscosity reduction in oil.